Initiation Of Emulsion Polymerization Research Articles

Controlled radical emulsion polymerization of polystyrene

In this paper, a new water-soluble initiator system, 2-bromopropane/CuSO4/sodium ascorbate, was used as the initiator for emulsion polymerization. Radical emulsion poly- merization of styrene was successfully carried out at 80 °C by using sodium dodecylbenzenesulfonate as the emulsifier. The 2-bromopropane/CuSO4/sodium ascorbate-initiated emulsion polymerization shows the controlled free-radical polymeriza- tion features with linear growth of molecular weight. Polysty- rene with a relatively high molecular weight and a narrow molecular weight distribution can be synthesized by this method. On the other hand, stable polystyrene latex can be obtained, and the size of the polystyrene latex increased with the increase in monomer conversion.

Synthesis and use of a surface-active initiator in emulsion polymerization under AGET and ARGET ATRP conditions

A novel surface-active ATRP initiator disodium 4-(10-(2-bromo-2-methylpropanoyloxy)decyloxy)-4-oxo-2-sulfonatobutanoate (1a) has been designed and synthesized efficiently in three steps. The controlled radical emulsion polymerizations of methyl methacrylate (MMA) were realized in one step without any added surfactant under AGET and ARGET ATRP conditions, in which the initiator 1 functioned as both an ATRP initiator and a latex stabilizer.

Organocobalt chelates as initiators of emulsion polymerization of styrene

The kinetics of decomposition of organocobalt chelates in the pH range of 2.2–7.0 has been studied. It has been shown that the rate constant of decomposition of the octyl chelate complex at 20°C changes from ∼3 × 10−3 to ∼6 × 10−6 s−1 in the above pH range. The rate constants of decomposition of complexes with ethyl, octyl, and cetyl ligands, as estimated at 20°C and pH 8.3, are 1.69 × 10−4, 1.39 × 10−4, and 2.42 × 10−5 s−1, respectively. As evidenced by emission spectrometry measurements, ∼100% of organocobalt chelates with ethyl and isopropyl ligands occur in the aqueous phase, while organocobalt chelates with octyl and cetyl ligands are partitioned between monomer and aqueous phases. The rates of initiation of the emulsion polymerization of styrene have been measured by the inhibited polymerization procedure. It has been demonstrated that among three tested compounds (diphenyl picryl hydrazyl, hydroquinone, and benzoquinone), benzoquinone has been found to be a suitable inhibitor for the polymerization under study. The rates of initiation of styrene polymerization at 30°C for organocobalts with ethyl, octyl, and cyclohexyl ligands are 1.0 × 10−7, 1.04 × 10−7, and 3.7 × 10−6 mol/(l s), respectively. The rate constant of decomposition of the organocobalt complex with the octyl ligand at 30°C is 2.28 × 10−5 s−1, and the efficiency of initiation with this complex is 0.95.

On the role of initiator in emulsion polymerization

The use of nonionic poly(ethylene glycol)-azo-initiators instead of ionic initiators in emulsion polymerizations offers interesting possibilities for modifying the colloidal and polymeric properties of polymer dispersions. Experimental results are presented for various kinds of anionic, cationic, and nonionic stabilizers as well as for peroxodisulfate initiators with different counter ions (ammonium and potassium). For example, in a styrene emulsion polymerization (with monomer to water mass ratio of 1:4 at a given concentration of 1% with respect to monomer mass of either an anionic or a cationic surfactant), the replacement of either peroxodisulfate or 2,2'-azobis(2-amidinopropane)dihydrochloride by a poly(ethylene glycol)-azo-initiator (with a poly(ethylene glycol) molecular weight of 200 g mol–1) leads to particles with considerably smaller size, polymers with higher molecular weight, and latexes with higher viscosity.

Recent advances in the preparation of latexes

The industrial production of latexes has grown from the first poly(butadiene-co-styrene) produced in the U.S. for synthetic rubber and the first poly(vinyl acetate) produced in Germany for adhesives to many different polymer families produced for a wide variety of applications. Both conventional (oil-in-water) and inverse (water-in-oil) emulsion polymerization comprise the emulsification of an immiscible monomer in a continuous medium, followed by polymerization with a free radical initiator, to give a colloidal sol of submicroscopic polymer particles smaller by an order of magnitude than the original emulsion droplets. Both processes give “emulsion polymerization kinetics,” i.e., a proportionality of both polymerization rate and number-average degree of polymerization to the number of particles, instead of the inverse relationship between these two parameters observed for mass, solution, and suspension polymerization. The emulsion polymerization process can be divided into particle nucleation and particle growth stages, and it can be carried out using batch, semi-continuous, or continuous processes. Seeded emulsion polymerization can be used to obviate the particle nucleation stage in all three processes. The mechanisms proposed for initiation of emulsion polymerization can be divided into four categories, according to the locus of particle initiation: 1) monomer-swollen emulsifier micelles; 2) adsorbed emulsifier layer; 3) aqueous phase: 4) monomer emulsion droplets. Three generations of latex development are defined, according to the emulsifiers used: 1) conventional emulsifiers; 2) functional monomers; 3) polymeric emulsifiers. The formation of coagulum (polymer recovered from the latex in a form other than stable latex) during emulsion polymerization is attributed to two causes: 1) a failure of the colloidal stability of the latex; 2) polymerization by a different mechanism, e.g., mass (monomer layer), surface (walls, roof, agitator shaft), vapor (atmosphere). The failure of the colloidal stability is attributed to diffusion-controlled, agitation-induced, or surface flocculation of the particles, according to the agitation rate (flow Reynolds numbers) and the power consumption (high Reynolds numbers).

The decomposition of potassium persulphate used as initiator in emulsion polymerization

AbstractThe decomposition rate of potassium persulphate in various aqueous solutions was measured by isotachophoresis using pure water, sodium dodecyl sulphate (SDS) solution, emulsifier‐free polystyrene emulsion, SDS solution containing acrylamide monomer or an SDS‐containing emulsion polymerization system for styrene. “Free” SDS molecules in the monomolecular dispersed state were found to increase markedly the decomposition rate, whereas those which formed micelles and became adsorbed onto polystyrene particles did not increase it. The acceleration phenomenon in the former case disappeared in the presence of a small amount of monomer.

An isotachophoresis for the microdetermination of potassium persulphate as initiator in emulsion polymerization

An isotachophoresis (IP) was applied to determine the decomposition rate of potassium persulphate (KPS) as initiator in emulsion polymerization, in comparison with conventional iodometry and ferrometry. For the exact determination, the latter methods needed several milliliters of the emulsion pipetted from the polymerization system, whereas IP did only a few microliters. Moreover, the amount of sulphuric acid produced as the decomposition by-product was simultaneously determined by IP, which is impossible for iodometry and ferrometry.

Initiation of emulsion polymerization by the redox system: titanium(III)-hydroxylamine

Polymerisation du styrene, acrylonitrile acetate vinylique, methacrylate de methyle et isoprene, a 30°C

ChemInform Abstract: MAGNETIC FIELD AND MAGNETIC ISOTOPE EFFECTS ON PHOTOINDUCED EMULSION POLYMERIZATION

The photochemically induced emulsion polymerization of styrene, methyl methacrylate, or acrylic acid is photosensitized by oil-soluble ketone initiators (e.g., dibenzyl ketone) to conversion and average molecular weights that are comparable to those achievable by employing conventional aqueous-soluble thermal initiators such as persulfates. The efficiency of polymerization and the average molecular weight of the polymers formed are significantly increased by the application of laboratory magnetic fields when photoinduced initiation is sensitized by oil-soluble ketones but not when aqueous-soluble thermal initiators are employed. With 1 ,l'-diphenyl- 1,l'-azoethane as initiator, triplet-sensitized initiation, but not thermal or direct photoinduced initiation, shows magnetic field effects on the average molecular weight and the yield of the products. No magnetic field effects are observed for photoinitiated polymerization of styrene or methyl methacrylate in toluene solution. With dibenzyl ketone that is enriched with I3C at both benzylic carbons as photoinitiator, the molecular weight distribution is bimodal. Varying the ratio of IT-enriched and natural-abundance DBK changes the relative yield of the lower and higher molecular weight fractions. It is concluded that external magnetic fields decrease the efficiency of triplet to singlet radical-pair intersystem crossing within micelles and accordingly increase the fraction of radical pairs that escape without terminating polymerization chains. An important characteristic of emulsion polymerization (EP) is the production of high molecular weight polymers at a relatively rapid rate.) The simultaneous achievements of high-molecu- lar-weight polymer and high polymerization rate result from the occurrence of initiation by single radicals at a large number of isolated microscopic reaction vessels (the micelle aggregates in- itially present), so that chain termination rates are decreased. Extensive work has been carried out on the mechanism of such polymerizations, and it has been found that, in general, water- soluble initiators are best suited for thermally initiating EP.' Oil-soluble initiators are commonly ineffective in EP either as thermal initiators or photoinitiators, presumably because such initiators produce pairs of radicals in the initial-polymerization loci and because these pairs undergo termination before substantial polymer growth can be effected.Id This result is generally expected if singlet radical pairs are generated in the initial bond-cleaving process. However, photochemically generated triplet radical pairs in micelles have been shown to survive long enough to compete, so that escape from micellar aggregates can compete with radical recombination in the mi~elle.~-~ Furthermore, application of relatively weak magnetic fields (GOO G) has been shown to substantially enhance the efficiency of escape of radicals from micelle aggregates. Since enhanced escape of a radical from a radical pair should increase polymerization rates and molecular weights in EP, we have explored (1) the influence of the application of weak magnetic fields on the rate of EP and molecular weight distribution (MWD) of polymers produced in polymerizations initiated by dibenzyl ketone (DBK) and other ketones that are known to produce triplet benzyl radical pairs in direct photolysis and by triplet sensitization of 1,l'-diphenyl- 1,l'-azoethane (DPAE) and (2) the I3C isotope effects on polymer molecular weight distribution produced by DBK photoinitiation. Results Comparison of Molecular Weights and Yields as a Function of Initiation Method. Since photoinitiation has not been commonly employed for initiation of EP, we have compared averaged polymer ~~~~

Emulsion Polymerization of Vinyl Monomers under the Influence of Ionizing Radiation

AbstractIonizing radiation induces the polymerization of some vinyl monomers in aqueous emulsion with high radiation yields. With identical emulsion compositions, the kinetics of this reaction and the kinetics of emulsion polymerization induced by water‐soluble initiators are very similar. The rate of reaction in emulsion polymerization is about one hundred times greater than in bulk polymerization. The initiation of emulsion polymerization by means of ionizing radiation permits uniform “illumination” of the reacting volume, as well as almost any desired variation in the frequency of initiation during the reaction. The sharp decrease in the overall rate of reaction when initiation is interrupted during emulsion polymerization of styrene induced by γ‐rays contradicts the earlier concept of sharply separated reaction zones.